Research On Mems Deformable Mirror Based On Polymumps Technology

Adaptive Optics (AO) has potential applications in many fields such as astronomical telescope, high energy laser, light beam combination, laser communication and medical ophthalmic detection. Miniaturized deformable mirror (DM) plays a key role in adaptive optics miniaturization and integration, as DM is one of key conponents in an AO system. This dissertation analysises the properties and fabrication techniques of various small DMs, and simulates the performances of bimorph DM and membrane DM. Compared with the others, the DMs fabricated with Micro Electro Mechanical System (MEMS) technology have the advatages of small volume, low power consume, low cost, fast response and integrated with microcircuit, as they have been deeply investigated. The fabrication technique and the preparation and performance of the materials commonly used in MEMS DMs fabrication are introduced in detail. With comparasion of the two commercial standard surface micromachining technologies, Poly Multi User MEMS Processes (PolyMUMPs) is chosen to be the fabrication technique of our MEMS DMs in the consideration of cost and research period.This dissertation mainly focuses on large stroke micro-mirrors based on technical characters and design principles of standard PolyMUMPs process. The influences of eching holes, surface roughness, print-through effect and residual stresses of different materials on mirror surface quality are investigated with the DM design requirements. Based on parallel plate actuator model, restrict of PolyMUMPs for achieving large stroke is discussed. Two designs of large stroke actuators are put forwarded originatively and low driving voltages and high mirror surface qualities are also considered in the permission of fabrication process. The actuated styles, mirror structure design method, simulations of electrostactic actuators and micro-mirrror, mirror performance test are also discussed in details.Two designs micro-mirror with large stoke—micro-mirror with cantilevers and micro-mirror with lever actuators are proposed. According to micro-mirror with cantilevers, the influences of residual stresses on the properties of mirror plate and cantilever are analyzed with finite element method and the optimized structure parameters of mirror plate and cantilevers are obtained. The elevated height of cantilever is calculated with analysis method and the results are compared with FEM. The static and dynamic characteristics of micro-mirror with cantilevers are analyzed. According to micro-mirror with lever actuators, minimized mirror plate with edge strengthing is designed to reduce the mirror plate deformation induced by residual stresses. Lever actuators with special shapes are also designed with layout smoothing method to reduce the print-through effect.The elevated heights and pull-in voltages with different constants of lever structures are simulated with FEM software Comsol, as a result, the dimensions of some important components of lever strucure are optimized.A multi channel high voltage control circuit is proposed and its amplification results are tested in lab envirement. Two design fabricated micro-mirrors are measured and analyzed with Polytec microsystem analyzer, Wyko optical profiler and I-V curve analyzer. The results of static and dynamic characteriscs of two designed micro-mirrrors show close consistency with simulation results, which prove that large stroke actuators can be achieved by PolyMUMPs process, but both high quality mirror surface and high fill-in factor are restricted which can be improved by combining with other porcesses. Some constructive proposals are put forward for designing and developing high performance MEMS deformable mirrors in the future.